Preparation Of Cr(Ⅵ) Adsorption Materials From Bagasse Modified By Biological Method And Its Effect Analysis

Hexavalent chromium(Cr(VI))is a toxic heavy metal ion widely present in the environment,which seriously endangers human health.Adsorption is one of the effective ways to control Cr(VI)contamination.Looking for a low-cost and efficient adsorbent is the key to the development of adsorption method to control the wastewater containing Cr(VI).Sugarcane bagasse(SCB),as a main by-product of sugar squeezing enterprises,has the characteristics of being cheap,easily available,recyclable,and renewable.Its main components include cellulose,hemicellulose and lignin,which has great potential as bioadsorbent for heavy metals.Most research focuses on improving the adsorption performance of SCB through physical and chemical modification,but it is easy to cause problems such as high energy consumption,cumbersome operations,and pollution of chemical regents.In order to reduce cost,pollution and energy consumption during the preparation process,based on the analysis of the composition of SCB,we used microbial treatment to modify the SCB to prepare bio-modified sugarcane bagasse(Bio-modified Sugarcane Bagasse,BMSCB).Firstly,by comparing the treatment effect of different strains,and exploring the relationship between the duration of microbial treatment and the adsorption rate of the resulting modified material,the best biological modification method was finally determined.Secondly,characterized the modification mechanism by analyzing the composition changes and surface structure characterization.Thirdly,the optimal conditions for the maximum adsorption of Cr(Ⅵ)by BMSCB were obtained through single factor experiments.At last,the adsorption mechanism was based on fitting of the static adsorption experiment with adsorption isotherms and adsorption kinetic curves.The main results and conclusions of this study were obtained as follow:(1)Established the bio-modification method of sugarcane bagasse.The combined treatment of SCB with Pectobacterium carotovorum HG-49 and Bacillus subtilis HR-5 during 24 hours at 37 ℃ increased the removal rate of Cr(Ⅵ)by 28.53%.The results of SEM,XRD,FTIR and BET show that the surface of the modified bagasse is smooth,the fibers are looser than untreated one,with more active groups,a larger specific surface area and more porous structures,which could conducive to the adsorption of BMSCB to Cr(Ⅵ).(2)The optimal conditions for adsorption of Cr(VI)by BMSCB were determined.Single-factor adsorption experiment shows that when the Cr(Ⅵ)content was 50 mg/L,the optimal contact time is 210 min,the optimal adsorbent dosage was 2.8 g/L.And in the p H range of the electroplating wastewater solution containing Cr(Ⅵ),which p H is about 2-3,always has a higher adsorption rate.The existence of other coexisting ions will not affect the adsorption effect of Cr(Ⅵ).Under the optimal adsorption conditions,the adsorption rate of BMSCB to Cr(Ⅵ)in the solution at a concentration of 50 mg/L can reach 92.64%.(3)The adsorption mechanism of Cr(Ⅵ)by BMSCB was analyzed by curve fitting of adsorption kinetics and adsorption thermodynamics.The static adsorption data is in accordance with the pseudo-secondary model.Which means that the adsorption of Cr(VI)by BMSCB is a chemically dominant mixed adsorption process and conformed to the intraparticle diffusion kinetic model;The results show that the adsorption rate is controlled by the diffusion of BMSCB surface membrane and pore size.The adsorption of Cr(Ⅵ)by BMSCB conformed to the Langmuir isotherm model,indicating that the adsorption process is endothermic and can spontaneously monolayer adsorption,calculated according to the model,the maximum adsorption capacity can reach 19.80 mg/g under the temperature condition of 25 ℃.In summary,BMSCB prepared with sugarcane bagasse as raw material shows considerable adsorption effect for Cr(VI).Compared with chemical modification and high-temperature carbonization modification,the biological modification process is mild and safe,and will not cause secondary pollution to the environment.It shows that BMSCB can be a green and low-cost adsorbent,which has superior application prospects in the treatment of wastewater containing Cr(VI),and also provides reference for the biological modification of other agricultural wastes to prepare heavy metal ion adsorbents.